Gas - Liquid Equilibrium Of Pb - Sn - Sb Ternary Alloy

It is very important to recycle the Pb-Sn-Sb alloys produced from the smelting process of Pb, Sn and Sb and their consumption process due to the rapid reduction of non-ferrous metals resources, the complexity and depletion of minerals and the severe environmental contamination. Vacuum distillation has many advantages such as short flow sheet, zero pollution and high metal recovery rate in disposing of the Pb-Sn-Sb alloys. The existing theory of vacuum distillation, however, still remain in the binary alloy systems, which cannot support the research of ternary and multi-component alloy systems. The prediction and experimental determination of activities of components of alloys will be carried out by taking the Pb-Sn-Sb alloy as the research project. Meanwhile, The vapor-liquid equilibrium (VLE) prediction model will be built up, and the corresponding experiments will be carried out for validation purpose in this work. The main research contents and conclusions of this work are as following:1. Firstly, the molecular interaction volume model, viz., MIVM was simplified, the activities of Pb-Sn alloy at 1050K, and of Pb-Sb and Sn-Sb alloy at 905K were then predicted by using the simplified MIVM, Wilson equation and Miedema model, respectively. The average relaive deviations and average standard deviations of all above models have been calculated, which indicates that the average relaive deviations of both simplified MIVM and Wilson equation were smaller than ±8.50%, the prediction deviations of them are in the same order of magnitude, the prediction accuracy of Miedema model with the average relaive deviation of larger than ±15.00% is relatively poor among these three models. Secondly, the model parameters of the simplified MIVM and Wilson equation were calculated in the temperature range of 1073K-1573K. Finally, the activities and activity coefficients of the above three binaries were predicted in the temperature range of 1073K-1573K by using the simplified MIVM and Wilson equation.The activities of components of Pb-Sn-Sb alloy were calculated by using the simplified MIVM and Wilson equation, respectively based on the parameters of the related three binaries in the temperatue range of 1073K-1573K. The simplified MIVM can be used to predict the thermodynamic properities of multi-component alloy systems without calculation of the coordination numbers and molar volume of liquid metals by using the infinite dilution activity coefficient γi∞, γi∞. Then, three ternary prediction models were obtained from the binary model by combining the Miedema model with Toop, Kohler and Chou’s model, respectively. Finally, the activities of components of Pb-Sn-Sb alloy were calculated by using the extended models in the temperatue range of 1073K-1573K.2. The activities of components of Sn-Sb alloy were determined firstly by using the Electromotive force (EMF) method with Yttria (8 mol%) Stabilized Zirconia (8YSZ) as solid electrolyte in the temperatue range of 905K-1073K (25K interval). The deviation between the activities determined in this work and that determined by using the molten electrolyte (LiCl+KCl+SnCl2) found in literature was smaller than 5% indicating that the EMF method with 8YSZ as solid electrolyte was reliable. Then, the activities of components of Pb-Sn-Sb alloy were measured by using the EMF method with 8YSZ as solid electrolyte in the temperatue range of 820K-1273K.3. The verification and filter for the simplified MIVM, Wilson equation and Miedema model was carried out by using the experimental data of activities available in literatures and determined in this work. The largest average relative deviation ws ±8.49% for the simplified MIVM, and ±5.90% for the Wilson equation. The prediction accuracy of the simplified MIVM and Wilson equation are basically the same. However, the MIVM has a clear physical basis and less empirical parameters was needed in the prediction process. The largest average relative deviation was ±19.52% for the Miedema model indicating that the prediction accuracy of Miedema was most poor among these three models. The above analysis indicates that the simplified MIVM was reliable for predicting the activities of components of Pb-Sn, Pb-Sb and Sn-Sb alloys.The verification and filter for the simplified MTVM, Wilson equation, Toop, Kohler and Chou’s model was also carried out by using the experimental data of activities determined in this work. The largest average relative deviation was ±10.30% for the simplified MIVM, and ±8.81% for Wilson equation. The prediction accuracy of the simplified MIVM and Wilson equation are basically the same, and both of them can conveniently predict the activities of muli-component alloys by using only the infinite dilution activity coefficient γi∞, γj∞ of the related binaries. However, the simplified MIVM has a clear physical basis and less empirical parameters was needed in the prediction process. In addition, the simplified MIVM can be reduced to Flory-Huggins, Wilson equation and NRTL, respectively under some special conditions. Moreover, it can meet the requirement of Gibbs-Duhem equation and can be used to describe the thermodynamic properties of partially miscible systems, for which Wilson equation cannot be used. The prediction deviations of Toop, Kohler and Chou’s model was larger than that of both the simplified MIVM and Wilson equation, and the largest average relative deviation of all geometric models were larger than ±15%. In addition, all geometric models don’t have a clear physical basis, and cannot be used in the partially miscible systems. The above analysis indicates that the simplified MIVM was the most reliable model for prediction of the activities of components of Pb-Sn-Sb alloy.4. The method for calculation of separation coefficient and vapor-liquid phase equilibrium was amended and perfected by using the simplified MIVM. The vapor-liquid phase equilibrium of Pb-Sn, Pb-Sb, Sn-Sb binary alloys and Pb-Sn-Sb ternary alloys were then calculated by using this new method.A new VLE prediction model of binary alloys was built up by using the simplified MIVM based on the VLE theory. Then, the VLE data were calculated by using this new model, and the VLE phase diagrams (including T-x(y) and p-x(y) phase diagram) of Pb-Sn, Pb-Sb and Sn-Sb binary alloys were then plotted by using the calculated VLE data.A new VLE prediction model for Pb-Sn-Sb alloy system was built up by using the simplified MIVM based on the VLE theory, the VLE data of Pb-Sn-Sb was calculated by using this new ternary VLE prediction model, and the VLE phase diagrams were plotted using the calculated VLE data. The optimal experimental condition of vacuum distillation can be determined firstly according to the product we wanted before experiments based on the VLE phase diagrams. In addition, the distribution of components of alloy dependence of temperature and pressure can also be analyzed based on the VLE phase diagrams. Above all, the distillation product component can also be quantitatively predicted with the VLE phase diagrams.5. The VLE was experimentally determined for Pb-Sb, Sn-Sb binary alloys and Pb-Sn-Sb ternary alloy. The comparison between the calculated results and the experimental VLE data shows that the calculated results match with the experimental data. In addition, the calculated results were compared with the industrial experiment data, which shows that the average standard deviation was 83.23 K for the VLE temperature, and 0.0434 for the vapor phase mole fraction, which indicates that the binary and ternary VLE prediction models built up in this work were reliable and can be used for instructing the industrial practices.The reliable thermodynamic model that can be used to predict the activities of components of Pb-Sn-Sb alloy was selected, the VLE prediction model for binary and ternary alloy systems in vacuum distillation were built up. Finally, the following important progress and innovations were obtained:(1) The MIVM was simplified, the prediction accuracy was improved and the universality of the MIVM was enhanced by simplifing the calculation process of MIVM.(2) The activities of components of Sn-Sb binary alloy and Pb-Sn-Sb ternary alloy were firstly determined by using the EMF method with 8YSZ as solid electrolyte in this work. The experimental activities were accurate and reliable, which will provide the reliable experimental data for the development and modification of thermodynamic models. (3) The reliable thermodynamic model that can be used to accurately predict the activities of components of Pb-Sn-Sb alloy systems were obtained, the VLE relationship was built up, and the VLE calculation model for ternary alloy systems were obtained.This work will enrich the thermodynamic data of multi-component alloys, improve and perfect the basic theory of vacuum distillation, and provide the reliable theoretical foundation for separation of non-ferrous metals alloys in vacuum distillation.